Temperature compensation



April 1951 R. w. ENGSTROM 2,547,379

TEMPERATURE COMPENSATION Fi led Aug. 18, 1.947

IIEA T ER SUPPL Y INVENTOR.

B gdjbfi Wingsimm' Patented Apr. 3, 1951 TEMPERATURE COMPENSATION Ralph Engst'rom, East Petersburg,

Pa., assignor to Radio Corporation of America, a corporation of Delaware Application August 18, 1947, Serial No. 769,269

01. sac-22).

3 Claims.

This invention relates to control devices for electrical systems and more particularly to temperature compensation control devices which may be used in voltage regulators employing thermionic tubes, in which precision control of the voltage is desired.

A number of circuits have come into use which require an unusually stable high voltage supply. One example of such a circuit would be the. plate voltage supply circuit for use with photomultiplier tubes. In the conventional voltage regulators of the prior art, difiiculty is experienced in maintaining the output voltage stable due to the thermal inertia of the cathode emission after a. voltage surge, which causes a transient shift of output voltage. Expensive and elaborate temperature. control circuits which have been proposed to compensate for thermal emission changes are unsatisfactory when precision control of output voltage is desired because of this thermal time lag. A a (mu). bridge type of voltage regulator compensates for this thermal lag somewhat, but a study of the output voltages has revealed that the transient voltage shift, during the time in which temperature equilibrium is being established, is still of such magnitude. as to be objectionable.

Another difficulty with a (mu) bridge type of voltage regulators in the prior art is, that rebalancing of the circuit is necessary when selection of the output. voltage is provided. The present invention, therefore, contemplates electronic voltage regulating apparatus in which the transient output voltage shift due to the thermal inertia of cathode emission is stabilized, and in which selection of the output voltage level is provided without need for circuit rebalancing.

One object of my invention is to automatically provide compensation for output voltage shifts in voltage regulator circuits caused by the thermal inertia of the cathode. Another object of my invention is to compensate automatically for the. shifts in voltage caused bythe loss of cathode emission in the aging of vacuum tubes.

A further object of my invention is to provide in a voltage regulator circuit a simple thermal responsive device for regulating the output voltage level Without unbalancing the circuit. 7

Briefly, one, specific. embodiment of my presentinvention' which I have used for. the. purpose of illustration comprises a ,u (mu) bridge type of voltage regulator circuit in. which an additional vacuum tube is used to compensate for transient shifts in output voltage caused by thermal lag in. the emission after an input. voltage surge, and in which there is afforded a method of, controlling the output voltage level from the regulator without unbalancing the system.

The features of my invention which I consider novel are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying draw ings wherein lize reference characters designate similar parts throughout and in which:,

Fig. 1 is a schematic diagram of; a specific embodiment of my invention and,

Fig. 2 represents schematically a thermal compensating circuit.

Referring more particularly to Fig. 1, there is shown a I (mu) bridge type of circuit, which is adapted to maintain a constant voltage across an output circuit.

A high voltage unidirectional source of supply is indicated at the input terminals, l and 2, across which is connected a first voltage divider, 34-5, and a second voltage divider, 'i-B, in which the variable resistors, 5, and 8, are connected to the negative terminal, I, and the resistors, 3 and 7, are connected to t e positive terminal 2. A stabilizing vacuum tube, [1, is, provided, having its control electrode, M, connected to the control arm of the variable resistor 5, across which a neon tube or other constant voltage device is connected, its antde, it, connected through a resistor, [9, to the positive input terminal, and its cathode, 55, connected to the junction of resistors '1' and 8. Output voltage is obtained at terminals 29 and 2! from the plate resistor, 59, across which is connected a capacitor l8. A thermal compensating tube, I0, is also provided, having its control electrode, [2, connected at the junc ion of resistors l and 8, its anode, H, connected, at the junction of resistors 3 and 4 and its cathode, l3, connected through a variable resi'tance, 9, to the jmiction of resistors 7 and 8.

Voltage fluctuations which are compensated for by the effect of the voltage drop across resistor, 8, which is in both the bias circuit and the. discharge path of thestabilizing tube, keep the voltage across the, load resistor, i9, constant. There is, however, a lag in the emission change due to thermal inertia of the cathode, and it is found that when the ratio of resistances 8- to 1' is. correctly adjusted for input voltage fluctuations, the compensating effect, of the, cathode emission 2,547,379 1 I! i v across the resistor, 9, is applied to the control electrode, 12, of the thermal compensating tube to give an increased sensitivity to thermal emission changes.

The amplification factor a (mu) of the stabilizing tube is changed (via the voltage developed in resistor 8) in accordance to the input voltage fluctuations to provide a stabilized output voltage in the output resistance, !9. Residual output voltage fluctuations are filtered by the capacitor, i8, connected across the output. The circuit may be balanced for constant output current, so that small variations in load resistance are reflectedas nearly proportional changes in output voltage when the ratio of resistance 8 to resistance .1 is equal to the operating amplification factor of the tube. Because the amplification factor is primarily determined by tube geometry and because the net voltage drop between the cathode and grid is small in comparison to the input voltage, the circuit will remain in approximate balance for reasonable variations in the input voltage.

The ratio of resistances 4 to 3 should equal the ratio of resistances 8 to '7 so that the plate voltage variations on the thermal compensating tube, ill, will be a minimum, and the thermal compensating tube should be operated near saturation to furthenkeep plate voltage changes from changing its plate current.

Output voltage variations due to thermal changes may be brought to a balance in this circuit by adjusting the cathode bias of the thermal compensating tube with the variable resistor, 9. Adjustment of the output Voltage level, is obtained by varying the direct current bias of the stabilizing tube with the variable resistor, 5, which results in a change of space current through the resistor, l9, and a correspond ing change of output voltage.

When a tube with a flat a-Ip characteristic such as a 6SF5 or 6SL7GT is used as the stabilizer tube, a change of plate current corresponding to change of grid bias will not unbalance the circuit. If each half of the latter tube, or of any other double triode, is used in its respective circuit, the series filament connection additionally assures simultaneous thermal characteristics and a better resulting voltage output. This circuit is excellent for high voltage-low current applications because receiving type tubes canbe-used with-voltages in the order of 2,000 to 3,000 volts without exceeding their normal ratings, since the greater part of the voltage is dropped across the output resistor, 19, and the bridge resistor, 8, leaving only a portion of the voltage drop across the tube.

Further, the internal resistance of the circuit from the output side is high, being given by the series combination of resistor, i and the variational Rp (plate resistance) of the stabilizer tube.

The circuit is also particularly adapted to any application in which a common input and output positive potential is required or-in which the positive side at ground potential is recommended. It is shown in Fig. 2, that application of the thermal compensating tube is not limited to a a (mu) bridge type of voltage regulating circuit but may be adapted to any other circuits which require compensation for thermal emission changes caused by filament voltage fluctuations. Referring to Fig. 2, a thermal compensating tube, I0, is provided havin its anode, ll, connected to the positive side, i, of a unidirectional input potential through a resistor 25; its control electrode, l2, connected to the negative side, v2, of the input potential, its cathode connected to the negative terminal, 2, through a resistor, 9, which may be variable, and its filament, 24, connected to a voltage source which is shown as a transformer, 23. Output terminals, 26 and 21, are connected across the resistor 25.

Operation of the tube as a thermal compensator dependsupon a change of filament voltage (Ei) to change the output voltage (E0). By operating the tube at saturation any change of plate voltage upon the output voltage will be eliminated. A filament voltage change will change the cathode emission and the resulting space current flow through the resistor, 9, will cause an increased sensitivity to the change.- If the resistor, 9, is variable the magnitude of the output voltage may be adjusted.

Although I have illustrated a triode, it will be obvious that a diode could be used as a thermal compensating tube, iii, if the voltage gain obtained by utilizing the amplification factor of a triode or pentode were not necessary. In order to make the output voltage proportional to the changes in filament emission, when not operating the'compensatingtube at space saturation, a constant voltage supply is preferable. When all circuit elements may be considered constant the output voltage (E0) is determined entirely by the emission of the cathode, it, in the thermal compensating tube and this voltage may be ap plied to any circuit in which such a voltage is desired. I

It is to be understood that in the specific embodiment of my invention herein submitted there may be suggested to those skilled in the art certain modifications which will not necessarily constitute a departure from the spirit and the scope of my invention. Having thus fully described the nature, construction, and operation of my invention, I wish to secure by Letters Patem, and claim; 1. In a voltage regulator, a voltage source, a stabilizing tube having, an anode, a cathode and control electrode, a bridge circuit having two pairs of arms to which said supply source is connected, a circuit utilizing a portion of potential developed across said bridge circuit to bias said control electrode, an impedance connected between said anode and one side of said input voltage source, a thermal compensating tube having acathode and a control electrode, a cathode impedance for said thermal compensat ing tube, a voltage supply circuit for said thermal compensating tube derived from intermediate points on said two pairs of arms of said bridge, and a bias voltage for the control element of said thermal compensating tube derived -'from-said cathode impedance. 2. An automatic emission compensation circuit com'prising a bridge arrangement having an adjustable arm, a unidirectional voltage source connectedto said bridge arrangement, a stabilizing tube having a control electrode, an anode and a cathode, a load impedance, a circuit connecting said impedance between said anode and the positive side of said supply source, a circuit providing a bias for said control electrode from said adjustable arm, a thermal compensating tube having a cathode and a control electrode, an adjustable impedance connected in the cath ode circuit of said thermal compensating tube, a circuit connecting said control electrode of the thermal compensating tube to said adjustable impedance, and a circuit connecting the discharge path of said thermal compensating tube to intermediate points on said bridge arrangement so as to bias said stabilizing tube.

3. An electrical system comprising, in combination, a unidirectional input voltage supply source, a load impedance, a first voltage dividing impedance connected across said input voltage source, a second voltage dividing impedance connected across said input voltage source, a circuit deriving a biasing voltage from part of said first voltage dividing impedance, a constant voltage device controlling said biasing voltage, a pair of vacuum tubes each having a cathode, an anode, and a control electrode, a common cathode heatin voltage supply for said tubes, circuits connecting said plate of the first said tube to the one side of said load impedance, said cathode of said first tube to said second voltage dividing means, and said grid of said first tube to said constant biasing voltage, a circuit commonly connecting the positive side of said input voltage to the other side of said load impedance, circuits connecting said anode of said second tube to said first voltage divinding impedance, and said cathode to said second voltage dividing impedance, a cathode impedance for said second tube, a circuit deriving biasing voltage for said second tube from said cathode impedance, and a storage device connected across said load impedance.

RALPH W. ENGSTROM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,480,418 Paradise Aug. 30, 1949 FOREIGN PATENTS Number Country Date 638,748 Germany Nov. 21, 1936 655,376 Germany Jan. 14, 1938 OTHER REFERENCES Publication: Current Stabilizers, pp. 415-418, Proceedings of the I. R. 13., vol. 32, No. 7, July 1944. 

